This invention relates to materials which are ink jet imprintable and that can be used for adhesive image transfer, and constructions made with such materials.
Labels, tapes and similar constructions are ubiquitous in modern society. Many such constructions include a release liner coated with an adhesive, such as a pressure-sensitive adhesive (PSA), which is laminated to a paper or film face stock. Removal of the release liner allows the construction to be adhered to a substrate. The face stock and liner are a major cost of the label.
Many adhesives, such as those commonly used in label constructions, are not water dispersible or repulpable. Therefore, they make recycling of the label product difficult, due to the tendency of the adhesives to form globules during the repulping process. In addition, most PSAs are tacky when dry and cannot readily be used with ink jet printers that have become so popular in today""s world. Moreover, such PSAs typically are not hydrophilic, making it difficult to directly print on them directly with water-based ink jet printer inks. Instead, only the face stock or liner is ink receptive. The unsuitability of such PSAs for use in ink jet printers is compounded by the tendency of the adhesives to block the printer ports in the printers.
Although attempts have been made to formulate moisture activated or water activated adhesives, many of the adhesives produced have been rubber based and, therefore, subject to oxidative and UV degradation. Other adhesives have been solvent borne, and thus objectionable for environmental, health and safety reasons. The following patents are representative. U.S. Pat. No. 3,681,179 to Theissen discloses a solar control film construction having a water-activatable adhesive system comprising a normally tacky and pressure-sensitive adhesive coating covered by a thin, tack-free continuous water-soluble layer. A tack free emulsion acrylic adhesive is not disclosed.
European Pat. Nos. 199,468 and 297,451 describe a method for compounding water-activatable hot melt adhesives comprising polyaklylenimine or other vinyl heterocyclic monomers, a hydroxy-substituted organic compound, a plastizier, tackifier, and filler, and an antioxidant. No mention is made of making water activatable emulsion acrylic adhesives.
U.S. Pat. Nos. 4,331,576 and 4,325,581 to Colon et al. disclose common water-soluble hot melt adhesives based on polymers containing vinyl pyrrolidone and other heterocyclic monomers. Emulsion acrylics are not disclosed.
U.S. Pat. No. 4,052,368 to Morrison and U.S. Pat. No. 4,172,824 to Harrington describe water sensitive hot melt adhesives including polyester-based adhesives which typically comprise a copolyester in combination with a plasticizier. The systems are not emulsion acrylics.
None of the above-identified patents disclose or suggest the possibility of making a hydrophilic, acrylic emulsion polymer that is non-tacky when dry and water activated to become an adhesive, and that can be used in a xe2x80x9clabel-lessxe2x80x9d or xe2x80x9cliner-lessxe2x80x9d construction, i.e., a construction in which either a face stock or liner is not required
Many arrangements for the transfer of images from ink jet printers are known. For example, images, including printing, may be printed onto labels having pressure sensitive adhesive on the labels, and these labels may be applied to a desired substrate, such as a bottle or other product.
In accordance with the present invention, it has been determined that some unique benefits may be obtained by imaging onto a polymer layer, coated on an opaque or transparent plastic sheet, such as MYLAR(trademark), as a base layer, using an ink jet printer.
A conventional ink jet printer is employed to apply an ink image, preferably a colored image, to the adhesive layer of an image transfer sheet, the adhesive layer having been coated onto a base layer which is preferably flexible and nonporous to an ink jet printer ink. The non-porous flexible layer may be a sheet of plastic which can be either opaque or transparent.
The adhesive layer is compatible with and will absorb an ink jet printing ink. Most inks used in ink jet printers are water based, but such inks may also be based on organic solvents or carriers for the ink dyes and/or pigments. Thus, depending upon the ink used in the ink jet printer, the adhesive layer may be either hydrophilic or hydrophobic. Since, as noted above, most ink jet printing inks are water based, it is generally preferable if the adhesive coating or layer, at the time of imaging, is hydrophilic and will absorb the water-based ink.
Water-based inks for ink jet printers are well-known in the art and therefore no detailed exemplification thereof will be given herein. These water-based inks contain a sufficient amount of water to be the carrier for the dyes and/or pigments in the ink. Of course, a water-based ink jet printing ink may contain water-miscible organic liquids such as polyhydric alcohols which are often present in water-based inks to prevent clogging of the nozzles. The inks may also contain a variety of other compounds such as surfactants, etc.
At the time of printing the ink on and into the adhesive layer to form an image, the adhesive layer should be detackified. After the adhesive layer is imaged, it will then be activated, i.e. the adhesive layer tackified to a tacky state, and adhered or bonded to any desired substrate such as a ring binder, clothing, notebook cover, a glass window, a wall or anywhere it is desired to view the image. In this regard, it should be noted that if the image is placed or adhered to a non-transparent substrate, and the base layer is not transparent, the adhesive layer should be releasably bonded to the base layer so that the base layer can be removed to allow the image to be seen by a viewer. From the foregoing, it is apparent that the image is viewable from both the lower surface (i.e. the surface facing the base layer) and the upper surface (i.e. the surface facing away from the base layer) of the adhesive coating or layer.
The ink absorbing adhesive layer used in the present invention may be pressure sensitive, particularly hydrophilic pressure sensitive adhesives. Such adhesives are known in the art and include repulpable pressure sensitive adhesives such as those disclosed in U.S. Pat. Nos. 5,196,504 and 5,326,644, such disclosures being incorporated herein by reference. The adhesives disclosed in these patents are water-dispersible and tacky at room temperature which make them ideal for use in the present invention. Of course, other pressure sensitive hydrophilic adhesives are also known in the art and they too are suited for use in the present invention.
If an adhesive is used which is tacky at the time when it is imaged, the adhesive may be detackified by providing the imaging transfer sheet with an outer detackifying layer over the upper surface of the adhesive coating. Such a detackifying layer will be porous to the imaging ink so that a sufficient amount of ink will pass through the porous detackifying layer to the adhesive layer to allow an image to be formed therein. Generally speaking, the detackifying layer will permit at least 30 percent and preferably more (e.g. 40 percent) of the ink jet printing ink to pass into the adhesive layer and form an image.
Various types of porous detackifying layers may be used. For example, a mesh coating such as cheesecloth may be used, preferably with a very thin layer of release material such as silicone between the mesh layer and the adhesive, preferably coated on the mesh before it is applied to the adhesive so that the mesh layer may be more readily removed. It is emphasized that the silicone layer does not cover the pores of the mesh, thereby allowing the ink to pass through the pores of the mesh and into the pressure sensitive adhesive. Other mesh materials having finer strains and being less coarse than cheesecloth may be employed. Even paper may be employed since it is porous to the ink.
Other porous detackifying outer layers which are useful in the present invention may be formed from finely divided particles uniformly dispersed on and bonded to the surface of the tacky adhesive layer. Examples of such particles are cellulose particles and dextrin particles. It is particularly preferred if the finely divided particles have the shape of round spheres as is the case with starch particles (e.g. corn or potato starch) and powdered polyvinyl alcohol. Such porous layers are advantageous used with a pressure sensitive adhesive which, when heated, becomes sufficiently fluid that when pressure is applied the particles are dispersed into the adhesive layer, thus allowing the tacky adhesive layer to contact and adhere to a suitable substrate. If the finely divided particles have substantially the same refractive index as the adhesive layer (e.g. starch particles and polyvinyl alcohol particles), the particles are not seen by a viewer and thus seem to disappear. Exemplary of pressure sensitive adhesives which are well suited for use with the finely divided particles are repulpable adhesives as described in the patents cited above. It should be noted that powdered vinyl alcohol (whether in the form of round spheres or not) is normally not tacky when dry, but is permeable to water so that the ink jet image is readily absorbed into the PVA coated pressure sensitive adhesive. Where this detackifying coating is used, it is desirable to wet or at least dampen the substrate to which the image is subsequently applied, or the PVA surface, and this serves to activate the adhesive and have the PVA combine therewith.
It is also noted that a release layer may be employed between the adhesive and the non-porous, flexible, preferably transparent, backing sheet, so that the backing sheet may be removed. When a hydrophilic adhesive is used and the image sheet is adhered to a window, for example, it may be washed off by first removing the transparent plastic sheet and then washing with soap and water in a normal manner.
In some other cases, it may also be desirable remove the transparent plastic layer, which may be MYLAR(trademark), for example, so that the image in the adhesive appears brighter; and an additional transparent detackifying layer, which may be polyvinyl alcohol, may be used between the release layer and the pressure sensitive adhesive to eliminate the surface stickiness or tackiness of the adhesive, which would otherwise be directly exposed. The detackifying layer need not be transparent, however, and may include fine metallic flakes, phosphorescent material, fluorescent material, fabric, leather, and/or other materials. The additional layer could also provide water proofing if comprised of urethane, varnish, or other water resistant material.
It is also noted that the pressure sensitive adhesive layer may be a delayed action, heat activated pressure sensitive adhesive wherein the pressure sensitive adhesive properties arise following heating and have a predetermined open tack time for adhering to surfaces, and then become non-tacky. When such a pressure sensitive layer is employed, a detackifying layer would not be needed. Examples of such adhesives include acrylates and ethylene vinyl acetate.
In accordance with another aspect of the invention, the upper layer of the image sheet may be a water activatable adhesive. In further accordance with the present invention, there are provided hydrophilic, repulpable, acrylic polymers which are non-tacky when dry but become tacky when wet, and which exhibit high peel strength and excellent adhesion to a diverse array of substrates, including paper, polymer films, and highly polar substrates such as stainless steel and glass. In one embodiment of the invention, the composition comprises an acrylic-based polymer prepared by emulsion polymerization of a monomer mixture comprising, based on the total weight of monomers, from about 40 to about 70% by weight of one or more alkyl acrylates, the alkyl group of which has from 4 to about 8 carbon atoms; from about 10 to about 20% by weight of methyl acrylate; from about 2 to about 15% by weight of vinyl acetate; from about 10 to about 25% by weight of methacrylic acid and/or acrylic acid and a positive amount up to about 30% by weight, of methyl methacrylate. In another embodiment, the monomer mixture additionally contains a positive amount, up to about 5% by weight, of a short chain hydroxyalkyl methacrylate, such as hydroxyethyl methacrylate. Unexpectedly, the presence of methyl methacrylate appears to enhance the xe2x80x9cclean breakxe2x80x9d between water-activated regions of the polymer layer and non-activated regions, a phenomenon described below.
The acrylic emulsion polymers of the present invention have a relatively high glass transition temperature (Tg)xe2x80x94as high as about 40xc2x0 C., for some formulationsxe2x80x94and a weight average molecular weight of from about 100,000 to about 200,000. Because of their high glass transition temperatures, the polymers are not tacky at room temperature, when dry. But the polymers are highly polar and, when exposed to moisture, such as the water in an aqueous ink jet printer ink, they become tacky, The polymers are hydrophilic and repulpable, water-activatable and transparent to visible light. They may be directly printed upon using, a water-based ink, and after activation and adhesion to a substrate can be removed from a substrate by application of water. They are particularly useful as ink jet-imprintable polymers converted into adhesives used in a variety of constructions, including xe2x80x9clabel-lessxe2x80x9d or xe2x80x9cliner-lessxe2x80x9d labels, security films, solar control films, beverage labels (where it is desirable to have a transparent label on a clear bottle), decorative adhesive image sheets, and the like.
This adhesive may be coated onto the flexible base layer, with an intermediate release coating, if desired. The resulting image transfer sheet is non-tacky when dry. However, the upper adhesive layer is hydrophilic, and will absorb an image from a conventional ink jet printer. Upon printing with the ink jet printer, the solvent present in the inks penetrates the mixture of PCA and polyacrylic acid causing the mixture to become tacky again, where the ink has been printed. The areas where ink has been printed will remain tacky until the ink solvent has evaporated. It is desirable to apply the image to the substrate while the printed areas are still tacky because once the ink has evaporated, the image sheet will again become non-tacky. However, if the ink dries, either the image sheet or the substrate, such as a window, may be sprayed or dampened with water to activate the adhesive so that the image sheet will adhere to the substrate.
In accordance with an improved embodiment of the present invention, an assembly for transferring ink-jet printed images has an adhesive layer in between a non-tack upper surface and a flexible substrate. The adhesive layer has discrete zones separated from one another along boundaries. The adhesive layer may either be printed in small dots, or may be printed as a continuous layer and then scored to form the discrete zones.
The user first prints an image onto the assembly with an ink jet printer, then places the upper layer of the assembly against an image-receiving surface. The user peels the assembly back from the image-receiving surface, thereby leaving the image on the image-receiving surface. The zones of adhesive into which ink jet printer ink has not been printed remain adhered to the flexible substrate, while the ink-bearing zones of adhesive attach to the image-receiving surface. This allows the image to break cleanly from the image sheet, which otherwise is prohibited by the cohesion of the acrylic adhesive layer.
In another aspect of the invention, an ink jet-imprintable, water-activated adhesive construction is provided. In one embodiment, the construction comprises a layer of water-activatable acrylic polymer, coated on a flexible substrate, which in some embodiments is a release liner, such as an inherently releasable film or a paper or film backing coated with a silicone or other release material. The water-activatable layer is non-tacky when dry, but becomes, tacky when exposed to water. Consequently, when printed with a water-based ink jet printer ink, the polymer layer becomes tacky within the region of the printed image, but not in regions not printed on. When applied to a substrate, this allows a clean break between imaged (printed) and unimage (unprinted) regions of the adhesive, and the ability to form a xe2x80x9clabel-less label.xe2x80x9d
The construction is useful as a label or decorative image sheet, and is applied to an object or surface by adhering the water-activated polymer (which is now tacky) to the object and, optionally, removing the flexible substrate. In one embodiment, the construction includes a water insoluble, transparent film layer, preferably of a polymeric material, disposed between the water-activatable polymer and a release liner. Alternately, the water insoluble layer is used in place of the release liner, as a flexible substrate.